With the availability and acceptance of fiber optic cables, comes the necessity of coupling light into and extracting light from the fiber optic cable. This entails the coupling of light, usually from a light emitting diode (LED), into the end of the fiber optic cable and the coupling of light from the end of the fiber optic cable to a photo-diode or other light detecting device. While fiber optic connectors which serve to position the fiber optic cable adjacent to such an active device have been known and utilized in the past, these devices have been relatively bulky devices. There is therefore a need for inexpensive miniature connectors to hold and position small diameter active elements, e.g. elements having diameters less than 100 mils. Prior art connectors include those illustrated in U.S. Pat. Nos. 3,878,397 issued to Robb et al, Apr. 15, 1975; 3,582,637, issued to John Cecil on June 1, 1971; 3,803,409, issued to Rudolf J. Prochauzka on Apr. 9, 1974; and 3,790,791, issued to Norman Anderson on Feb. 5, 1974. While the last of these two patents involve the modification of a standard connector, the modifications described in these patents require access to the interior of the connector which is to be modified. It will be appreciated that with subminiature light emitting diodes and photodetectors, it takes considerable time and effort to mount the active device within the housing of the connector. The difficulty stems from the limited clearance and limited access to the interior of the connector, as well as the small size of the devices to be mounted. Thus, in some cases the modification necessitates the use of tweezers which is, of course, an extremely time consuming process.
It will be appreciated that the length of time necessary to modify a connector materially affects the cost of the connector, and thus, if large amounts of time are expended in the modification, the modification becomes economically unfeasible.
Rather than mounting the active device within the modified connector housing, in the subject invention the active device is mounted at the end of the connector. This is accomplished by mounting the active device on a printed circuit (PC) board which has a metalized layer surrounding the active element. The printed circuit board is first drilled to provide a bore of the appropriate size and the active element inserted in the bore, with contact tabs at the face of the active element being soldered to the adjacent metalized layer. The PC board carrying the active device is then either silver epoxied or press-fitted onto the end of the female portion of a standard coaxial connector, with electrical contact being made from the tabs, through the metalizing layer to the metal casing of the female portion of the connector. The fiber optic bundle is inserted through the male pin of the male portion of the coaxial connector, such that when the two connector portions are mated, the end of the fiber optic bundle is aligned with and adjacent to the face of the active element.
Electrical connection to the active element is made via a lug which is carried by the casing of the female portion of the connector, and via an insulated wire or other conducting device, soldered to the contact at the back end of the active device.
For the modification, all that is necessary, therefore, is to remove the central pin or electrical contact from the female portion of the connector, enlarge the hole through which the pin originally protruded, drill a hole in a printed circuit board, punch out a donut shaped portion of the printed circuit board, with the bore concentrically carried, and either epoxy or press-fit the donut carrying the active device onto the end of the female connector. For applications in which many of the connectors are to be used together or "ganged", it is not necessary to punch out individual donuts. Rather, one PC board containing many active elements can be press-fitted to the backs of an equal number of connectors provided alignments can be precisely maintained. Generally, however, it is faster to use individually modified connectors ganged together. This avoids the problems associated with cumulative tolerances and also enables individual units to be more easily replaced in the event of failure of the active element.
In a hand operation, the entire modification takes place in under two minutes, though this time can be considerably improved upon with automated equipment.
A suitable miniature coaxial connector that is manufactured by many vendors is designated type SMC. This very inexpensive connector meets MIL SPEC MIL 39012/SMC. Typical manufacturers of this part are Automatic Connector, Americon/Omnispectra, and Sealectro. This connector is also called a TMM connector by some manufacturers. The barrel diameter of this connector is about 146 mils and the protrusion length is about 274 mils. The finished connector is thus about one seventh the cross section and one third the length of other fiber optic connectors. Because one of the big advantages of fiber optic cables is small size, with a connector of this size, it would be extremely difficult to make insertions into the connector body, which insertions would not only be time consuming and costly, but also might result in misalignment of the active element with the end of the fiber optic bundle.
It is therefore an object of this invention to provide a method for adapting a standard miniature coaxial connector for the coupling of fiber optic bundles or elements to an active element, either of the light emitting or light detecting variety.
It is another object of this invention to provide apparatus for quickly modifying a standard coaxial connector so that it may be utilized with fiber optic cables and active elements.
It is yet another object of this invention to provide an end-mounted active element configuration for the female portion of a connector in which the active element is to be optically coupled to fiber optic element or bundle; and,
It is a yet still further object of this invention to provide an economical fiber optic connector as a modification of a standard coaxial connector.
These and other objects will be better understood in connection with the following description taken in conjunction with the following drawings in which: